Doxy PEP For Preventing Sexually Transmitted Infections

While many people are familiar with PrEP for HIV prevention, not everyone is aware the antibotic doxycycline can be used to prevent STI’s. In particular, doxycycline can be useful in prevention of Syphiils, Chlamyida, and Gonorrhoea infections.

What is the level of protection?

Doxy PrEP is a good way to reduce the chance of STI’s however the degree of reduction is different for each disease.

Infection Reduction If HIV negative Reduction if HIV positive
Chlamydia 88% 74%
Syphilis 87% 77%
Gonorrhoea 55% 57%

Reduction in STIs when taking doxycycline within 72h post sex. 1

Efficacy against other bacterial STIs is not known, and doxy-PEP does not prevent HIV, monkeypox (MPX) or other viral infections, for example HPV and HSV. 2

How do I take doxy PrEP?

To take doxy PrEP you simply need to take 200mg of Doxycycline within 72h after sex. The earlier you take it the better however the effect is still present up to 3 days after sex.

If you have had sex multiple times in a day you only need to take the dose once. There is no need for more than 200mg of doxycycline in a day.

Side Effects

Doxycycline can be hard on the stomach occasionally causing nausea. It’s recommended to take it with some food to help line the stomach.

Doxycycline also can have a risk of red inflammed skin if you are exposed to sunlight. It’s recommended to avoid getting sunburned when taking doxy PrEP.

Is Doxy PrEP For Me?

If you have had multiple STI’s and feel you would like to reduce your chance of infection, talk wtih your doctor.

Of course while the chance of infection is reduced, the risk is not eliminated. Be sure to schedule a regular full sexual health screening. Your regular HIV PrEP appointment is a great chance to organise this testing.


  1. https://programme.aids2022.org/Abstract/Abstract/?abstractid=13231 ↩︎

  2. https://www.sfcdcp.org/wp-content/uploads/2022/10/Health-Update-Doxycycline-Post-Exposure-Prophylaxis-Reduces-Incidence-of-Sexually-Transmitted-Infections-SFDPH-FINAL-10.20.2022.pdf ↩︎